When estimating an orbit of an object which moves on an orbit (e.g. an artificial satellite and space debris) by using an optical observation equipment (e.g. an optical telescope), at least three coordinate points need to be specified. However, because the viewing angle is narrow in the optical observation equipment, it is difficult to detect three coordinate points of the object moving at high speed through once observation. Also, even if it is supposed that the three coordinate points of the moving object can be detected through the once observation by an observation equipment having the narrow viewing angle, the orbit estimated based on the coordinate points contains a large error.
For example, as shown in FIG. 1, in case of an optical telescope 101 having a relatively wide viewing field 110, three coordinate points 120-1, 120-2, and 120-3 of the moving object can be detected in the viewing field 110. In this case, an orbit 130-1 can be estimated by using the coordinate points 120-1, 120-2, and 120-3. However, when considering an observation error, the estimate orbit has an error in a range from an orbit 130-2 to an orbit 130-3. Because the coordinate points 120-1, 120-2, and 120-3 are detected in a narrow viewing field 110, the observation elongation α10 is small. Therefore, the error range exemplified as a range from the orbit 130-2 to the orbit 130-3 becomes large and the orbit estimation precision becomes low.
In this way, because the viewing angle of the optical telescope is narrow, it is difficult to estimate the orbit of the object moving at high speed. However, because the angle resolution of the optical telescope is high, it is desirable to estimate the orbit by using the coordinate points observed by the optical telescope, for orbit estimation in a high precision. For example, Patent Literature 1 (JP 2011-157030A) discloses a method of acquiring orbit data of a flying vehicle in a high precision by using a radar unit and an optical telescope.
Patent literature 1 determines an observation time and viewing angle of the optical telescope by using orbit 6 matters which are calculated based on a detection result by the radar. Thus, the monitoring by the radar with a low angle resolution can be made up, because it becomes possible to discover and track the flying vehicle moving at a high angular speed by using the optical telescope with the high angle resolution.
In Patent Literature 1, the radar monitoring precision can be made up but it is necessary to calculate the orbit 6 matters to determine an observation direction of the optical telescope. In other words, when carrying out a tracking observation by the optical telescope in order to improve the orbit estimation precision, the orbit 6 matters need to be calculated based on the radar detection result.
Also, in Patent Literature 1, whether the orbit of the monitoring object is known is determined based on the comparison result between the known orbits and an orbit which is estimated based on the detection result by the radar. However, because whether the monitoring object is known or unknown is determined after a specifiable orbit (whole orbit) is estimated based on the orbit 6 matters, the efficiency of the discovery of the unknown object is low.